Getter ion pumps



y 6, 1964 G. KlENEL 3,134,533

GETTER ION PUMPS Filed Aug. 17, 1960 United States Patent 3,134,533GET'I'ER ION PUMPS Gerhard Kienel, Hanau (Main), Germany, assignor to W.C. Heraeus G.m.b.H., Hanan (Main), Germany, a company of Germany FiledAug. 17, 1960, Ser. No. 50,121

Claims priority, application Germany Aug. 29, 1959 3 Claims. (Cl. 23069)The present invention relates to getter ion pumps, and has for anobject, improvements therein.

In pumps working with absorption substances which in recent times areused as getter ion pumps mainly with an ionization of the residual gasbut also as pure getter pumps without such ionization, vacuum is mainlyproduced and maintained in such a manner that getter material iscontinuously or intermittently vaporized and precipitated.

The getter material bonds a large part of the gases present during themovement of the atoms or molecules of the getter material due to thefact that they enter into a chemical combination with given types of gasmolecules, which combination precipitates in solid form. A further partof the residual gases is absorbed by the fresh surface of theprecipitated getter material. The gases which still remain, moreparticularly noble gases, are in many cases ionized by electronbombardment and the ions penetrate into the getter precipitate by meansof a suitable field distribution.

In proportion as the getter precipitate is saturated and therefore nolonger absorbs all the gas being set free in the vacuum vessel somegetter material is repeatedly vaporized by means of an automatic system,said getter material precipitating on the saturated layer, forming afresh surface thereon and taking up the residual gases to acorrespondingly high degree. ever very rapidly strongly saturated inmost cases because diffusion takes place from the previously saturatedlayer disposed thereunder into the new layer. Mainly the gases whichwere taken up by the old layer penetrate into the new layer and cause arapid saturation.

The invention has for its object to remove or minimise this drawback,and according thereto, at least after admission of air in the pump butpreferably also at certain periods of time during the operation, asubstance is vaporized on the precipitated layer of the getteringmaterial which prevents or at least strongly reduces a diffusion of gasmolecules or vapour molecules into the freshly vaporized layer, said gasor vapour molecules having been taken up by the existing layer of gettermaterial, especially of titanium metal.

For this purpose there may be used metals which vaporize well, whichshow at normal temperature very little tendency to chemical reactionsand are in part designated as noble metals. Such metals are gold,silver, platinum, ruthenium, rhodium, palladium, osmium and iridium.However, other metals also which are to a large extent chemically stablesuch as copper, nickel, cadmium, and tantalum may be used for thispurpose. In the cold state, the metal used should show no diffusion oronly a very small difiusion of gas molecules or gas ions through themetal. However, in the cold state it should also show no diflusion oronly a very small diffusion into the already present titanium layer or adiflusion of the titanium in the vaporized metal. In this connectionsilver in particular has proved excellent in practice, only a thin layerthereof substantially preventing any gas diffusion.

However, metal compounds also, mainly fluorides such as magnesiumfluoride or thorium fluoride may be advantageously used for thispurpose. The low electrical conductivity of these compounds is nottroublesome because the layers are very thin and the electrical currentto be conducted is relatively small.

The new layer is how- Patented May 26, 1964 The advantage of theproposal made here consists in a many times better utilisation of thegetter material present in the pump. In order to maintain a given vacuumfor a long duration a substantially smaller getter supply will thereforebe required in the pump.

However, the advantage of the invention is mainly noticeable when thepump must be flooded and the getter layer was completely transformedinto the oxide, nitride etc., by the atmospheric gases. Thereafter, whenthe operation is again started relatively thick new getter layers arenecessary in order to reduce the diffusion now occurring, to an extentsuch as to ensure a sufficient pump action. Hitherto it was thereforenecessary to remove the getter precipitate present substantially whollybefore flooding.

As a result of the present invention this is no longer necessary. Whenstarting the operation a substance hindering dilfusion, for examplesilver, is first vaporized and thereafter the getter material. It hasbeen shown that the pump then immediately reaches its normal pump actionwithout it being necessary to vaporize more getter material than isusual during the operation.

In order that the invention shall be more clearly understood, referencewill now be made to the accompanying drawings which show an embodimentthereof by Way of example and in which:

FIGURE 1 shows a getter ion pump according to the present invention inlongitudinal section, and

FIGURE 2 shows the layers vaporized on the wall, to an enlarged scale.

As shown in FIGURE 1, a getter ion pump consists of a tubular body 1,which has for example an internal diameter of 20 centimetres and is madeof stainless steel. This tubular part 1 carries at one end a flange 2which is connected by means of a metallic seal 3 to a flange 4 of a highvacuum vessel 5. The other end of the tubular part 1 is sealed by aplate 6. A pipe 7 leads from the body 1 through a valve 8 to asingle-stage or multi-stage vacuum pump schematically illustrated at 9.

Several electrical conductors lead through the tubular part 1 and thebase plate, said conductors being insulated from the electricallygrounded pump body by insulators 10 inserted in the wall of the body 1in a vacuum-tight manner.

Two Vaporizers 11 and 12 are situated within the pump body, each of saidVaporizers consisting of a heating wire, for example, made of tungsten.The tungsten heater wire of vaporizer 11 is surrounded by a thinnertitanium wire, and that of the vaporizer 12 is surrounded with a silverwire. An alternating current is passed to the Vaporizers 11 and 12 bythe leads 13 and 14 respectively as shown in the drawing, saidalternating current, on operation of switch 15 or 16, heating thetungsten wires in a known manner to such a temperature that the titaniumor silver coiled on it vaporizes. Further Vaporizers (not shown) areprovided for titanium, in the case when the pump is operated for alonger time.

Also within the pump body is situated a grid 25 having the shape of acircular cylinder, said grid being given a positive voltage relative tothe pump body 1 by means of the conductor 26, and being held byinsulators 27. Approximately in the axis of the pump is situated aheating wire 28 of tungsten, to which a current may be supplied by meansof the conductors 29. On operation of the switch 36, the heating wire 28is brought to a temperature such that it emits electrons. In the circuitshown it is at earth potential, like the pump housing, but it may have alower voltage relative to the pump body.

The pump works in the following manner:

The vacuum vessel 5 and the internal chamber of the pump are firstevacuated by the vacuum pumps 9, the

. 3 valve 8 being open. In order to remove the gases adsorbed on thewalls, the walls of the vessel 5 and also of the pump are then broughtto a higher temperature for example to 200 C. This may be efiected inany manner which is familiar to any'person skilled in vacuum technique,for example by heating coils (not shown) which for this purpose areapplied on the external side of the'vessel and of the pump. After acertain time the adsorbed amounts of gas are removed to a large extent.The valve 8 is then closed and the vacuum pump 9 is switched ofi. Thevaporizer 11'is now switched on and a given first amount of titanium isvaporized which precipitates on the pump wall 1 and reduces the pressurestrongly by gettering. Hereby nearly all gases which react chemicallyeasily such as oxygen, nitrogen and hydrogen etc.

are to a large extent removed;

Then the heating coil 28 is switched on and a positive voltage isapplied to the grid 25. The electrons pro-f duced by the heating element28 fly over to the grid 25, pass to a large extent through its meshesand before reaching the wall 1 are reflected by the field prevailingthere. They thus return again to the internal chamber of the grid 25 andcarry out an oscillatory movement in the manner described.

The electrons impinge in their long flight paths upon the residualmolecules of the vacuum and ionize them. The thus formed ions, mainlyions of noble gases are accelerated through the electrical field betweenthe grid 25 and the wall 1 and, are shot in the titanium precipitate onthis wall. This phenomenon leads to. a further very strong reduction ofthe pressure. After a certain time, the take-up capacity of the titaniumprecipitate is exhausted or at least strongly reduced, and therefore thepressure no longer drops further, but shows a tendency to rise. Thensome titanium is again vaporized on the saturated precipitate. Thissecond titanium layer is also saturated after a given time and thereforethe vaporization must be repeated.

It is not essential for the work of a pump that individual discretetitanium layers are precipitated in given intervals of time; thisillustration was only chosen for the purpose of a better understandingof the processes in the pump. The titanium could, on the contrary, bepractically continuously vaporized. Then also there occurs a saturationof the layers and therefore the rates of the vaporization must be chosento be suitably large.

However, as experience shows, the take-up capacity of the newly producedtitanium layers is smaller as would be expected according to knownchemical and physical considerations. This is obviously due to the factthat from the already saturated layers a part of the gases which arebound there, probably mainly hydrogen diffuses in the newly vaporizedlayer and saturates it to some extent beforehand. This reduces the'effectiveness of these layers. In order to' prevent this to the largestextent poslayer 37 is vaporized. The silver layer 36 prevents the 7molecules from difiusing from the lower layers 35 directly into the newlayer 37. The layer 37 is therefore avail- V able for the pressurereduction with all its absorption capacity.

I claim:

1. A vacuum pump comprising a housing having a pump chamber withsurfaces for receiving a getter material thereon and including an outletport and an inlet port, means for ionizing gas within said pump chamber,7

means for directing the travel of said ionized gas toward said surfaces,means for vaporizing a first getter material in said chamber for buryingsaid ions upon said surfaces, means for vaporizing a second getteringmaterial after a plurality of layers of said first material haveaccumulated upon said surfaces, said second material comprising asubstance which inhibits the diffusion of gas molecules'therethrough. a

2. A vacuum pump comprising a housing having a pump chamber withsurfaces for receiving a getter material thereon and including an'outletport and an inlet port, means for ionizing gas within said pump chamber,means for directing the travel of said ionized gas toward said surfaces,means for vaporizing'a first getter material in said chamber for buryingsaid ions upon said surfaces,

means for vaporizing a second gettering material after a plurality oflayers of said first material have accumulated upon said surfaces, saidsecond material comprising a metal chosen from the group gold, silver,platinum, ruthenium, rhodium, palladium, osmium, and iridium and whichinhibits the diifusion of gas molecules therethrough. V

3. A vacuum pump comprising a housing having a pump chamber withsurfaces for receiving a getter mate rial thereon and including anoutlet port and an inlet port, means for ionizing gas within said pumpchamber, means for directing the travel of said ionized gas toward saidsurfaces, means for vaporizing a first getter material in said chamberfor burying said ions upon said surfaces, means for vaporizing a secondgettering material after a plurality of layers of said first materialhave accumulated upon said surfaces, said second material comprising ametal compound chosen from the group magnesium fluoride and thoriumfluoride and which inhibits the diffusion of gas molecules therethrough.

No references cited.

1. A VACUUM PUMP COMPRISING A HOUSING HAVING A PUMP CHAMBER WITHSURFACES FOR RECEIVING A GETTER MATERIAL THEREON AND INCLUDING AN OUTLETPORT AND AN INLET PORT, MEANS FOR IONIZING GAS WITHIN SAID PUMP CHAMBER,MEANS FOR DIRECTING THE TRAVEL OF SAID IONIZED GAS TOWARD SAID SURFACES,MEANS FOR VAPORIZING A FIRST GETTER MATERIAL IN SAID CHAMBER FOR BURYINGSAID IONS UPON SAID SURFACES, MEANS FOR VAPORIZING A SECOND GETTERINGMATERIAL AFTER A PLURALITY OF LAYERS OF SAID FIRST MATERIAL HAVEACCUMULATED UPON SAID SURFACES, SAID SECOND MATERIAL COMPRISING ASUBSTANCE WHICH INHIBITS THE DIFFUSION OF GAS MOLECULES THERETHROUGH.